Active surveillance study on the safety of single versus concomitant administration of Diphtheria, tetanus and acellular pertussis combined vaccine following the immunization schedule adjustment

The overall incidence rates of adverse reactions were 12.12% (218/1,799) for single administration and 11.59% (358/3,088) for concomitant administration, with no statistically significant difference (χ²=0.30, P=0.583). No significant differences were observed between the two groups in local versus systemic adverse reactions, severity grades (grades 1~4), onset time (≤30 min, 31 min~7 d, 8~30 d), or dose sequence (doses 1~5).

For the major adverse reactions including pain, induration, swelling, and fever, no significant differences were found between the two groups. Within the concomitant administration group, the incidence rates of adverse reactions when DTaP was co-administered with one or two other vaccines showed no significant differences compared to single administration.Conclusion Following the 2025 DTaP immunization schedule adjustment, concomitant administration did not increase the risk of adverse reactions in children aged 2 months to 6 years, supporting the continued promotion of concomitant DTaP vaccination strategies.